At present, two different types of grinding machines are in common use for grinding the opposite faces of small parts such as engine connecting rods and the like. In the case of planar, or flat, connecting rods in which the faces of the opposite ends lie in common parallel planes, the faces may be ground on a double disc grinder in which a rotary feed wheel passes between two grinding wheels carrying the connecting rods to be ground so that the faces of both ends are ground in common planes at the same time. In the case of stepped connecting rods, which have different dimensions between the faces of the opposite ends, use of a double disc grinder is not practical. However, such stepped connecting rods may be ground on a multiple vertical spindle center column grinder in which only one side of the rod is ground at a time, separate wheels being provided for grinding the faces of the stepped opposite ends.
Thus, a double disc grinding machine works well on flat sided, or planar, rods but cannot be used in its present form for stepped rods. On the other hand, a center column grinder can be used to finish either stepped or flat sided rods but, in both cases, requires that the sides be finished separately and that the part be turned over between these finishing steps.